His closing comments mention that this display will only work for around 27 years but he figures he can always build a bigger display. We’d keep this around, physically unaltered for sentimental value, but switch to a hexadecimal readout to track just over 179 years. Maybe that’s a bit too geeky.

The RF module is what I’d use too – it’s foolproof one it picks up the Frankfurt long wave signal, no matter how many days the battery may have been out – and this is the kind of application where you do NOT want mistakes.

But I would have made it a bit more private – display embedded INTO the box, so you see it when you lift the lid (sensed with a magnet embedded in the lid, hall sensor in the box itself). The battery would last way longer, and you could have that extra bit of “fridge magic” never quite knowing what the display does with the lid closed.